Prime Minister Theresa May will visit Wales on Monday as part of a plan to engage with all the nations of the United Kingdom before she formally launches Britain's departure from the European Union.

May is due to trigger Article 50 of the EU's Lisbon Treaty, beginning two years of formal divorce talks, by the end of this month, and her office said she would be visiting Wales, Scotland and Northern Ireland to hear people's views.

Last year'sBrexitreferendum exposed splits that could threaten the unity of the UK, with Scotland and Northern Ireland delivering pro-EU majorities but finding themselves outvoted by the English and Welsh, who were in favour of leaving the bloc.

In a sharp challenge to May, Scottish First Minister Nicola Sturgeon said last week she would be pushing for a fresh independence vote after having been met by "a brick wall of intransigence" in London when seeking for Scotland to have its ownBrexitdeal. May rebuffed that, saying now was not the right time.

Northern Ireland's largest Irish nationalist party Sinn Fein has also said it wants a referendum on splitting from the United Kingdom "as soon as possible" to unite with the Republic of Ireland.

On Monday May andBrexitminister David Davis will meet with Welsh First Minister Carwyn Jones and business representatives to discuss how Wales can make the most of opportunities offered byBrexit, her office said.

"PRECIOUS UNION"

"From my first day ... I made clear my determination to strengthen and sustain the precious union. I have also been clear that as we leave the European Union I will work to deliver a deal that works for the whole of the UK," May said in a statement before the visit.

"I want every part of the United Kingdom to be able to make the most of the opportunities ahead and for Welsh businesses to benefit from the freest possible trade as part of a global trading nation."

The Institute for Government (IfG) think-tank warned on Monday, however, that there was "a complete lack of clarity" about the role Britain's devolved legislatures in Scotland, Wales and Northern Ireland would play in theBrexitprocess.

In a report, it also said that legislating to deliverBrexitwould place a huge burden on parliament, leaving it little time for anything else, and with a risk that laws could be passed without adequate scrutiny.

"The attitude that the Scottish National Party takes to the passage ofBrexit-related legislation in Westminster could affect the smoothness with which that legislation passes through parliament if they join forces with the (opposition) Labour Party and Conservative rebels," the IfG said.

Britain might need to pass up to 15 new bills before the Article 50 process is completed, the IfG said, on top of the Great Repeal Bill which will remove European Union directives from existing British legislation.

"It will be a challenge for both the government and parliament to do all this while still ensuring full scrutiny and leaving room for the government’s domestic policy agenda," said Hannah White, IfG Director of Research.